i purchased this one, SP-7265RP. I have only used it a few times. It has been great to use. I bought mine new for $19.00, but it is even cheaper right now. I have bought several item from National Tool Warehouse, all good transactions.
SP Air 7265RP
I purchased a Hot Water Heater element and Thermostat from the big box store. Printed a 3D bracket with accommodations for a switch and a cover. Used High Temp Permatex (probably did not need High Temp) to secure it all to the 20 gallon square tank parts washer.
Takes about 20 minutes to heat...